Many bacteria have evolved mechanisms to invade eukaryotic cells and survive intracellularly. After cell invasion, bacteria use a variety of mechanisms to evade degradation. Initially, bacteria are sequestered into an endosome-like vacuole. Some pathogens, such as Actinobacillus actinomycetemcomitans, Listeria monocytogenes, Rickettsia and Shigella, lyse the vacuole and enter the cytoplasm. However, some intracellular pathogens reside within vacuoles that mature through the endocytic pathway and are modified to prevent lysosomal fusion and acquisition of hydrolytic enzymes. A third group of bacteria that includes Brucella abortus, Legionella pneumophila and Porphyromonas gingivalis infiltrate the autophagic pathway during their intracellular life cycle.
Autophagy is an essential cellular pathway for the degradation of macromolecules and recycling of anabolic precursors such as amino acids. This pathway is useful in the removal of protein aggregates present in a number of neurological disorders and is essential for the survival of breast carcinoma (e.g., MDA-MB468 and MDA-MB231), osteosarcoma (Saos-2), and hepatoma (HuH7) cell lines when deprived of amino acids and serum growth factors.